The ability to measure the amount of carbon dioxide dissolved in a liquid is important for quality control in the carbonated beverage industry. Up to now, the only available methods for making this determination have involved the piercing of a sealed container. For example, U.S. Pat. No. 3,958,448, issued to Willis et al, discloses a pressure test method and apparatus in which a needle pierces the container. It has been common in the past to determine the volume of carbon dioxide in a bottle of a carbonated drink by putting a pressure gauge in communication with the bottle contents via a hollow needle inserted into the bottle.
These methods destroy the seal between the contents of the container and the outside atmosphere, thus rendering the bottle useless for further tests at a later time. Consequently, to test the shelf life of a bottled carbonated beverage is difficult and expensive since the same bottle or bottles cannot be tested repeatedly to determine the carbon dioxide content of the beverage as a function of time. This determination has become increasingly important since the advent of thin-walled plastic containers which are considerably more pervious to gases than the glass containers which have been used for carbonated beverages in the past.
It is an object of the invention to provide a method for determining the amount of a gas dissolved in a liquid in a thin-walled container without destroying the container by piercing it. It is a further object of the invention to provide a method for determining the amount of gas dissolved in a liquid in a thin-walled container to a high degree of accuracy. Such a method will make the determination of shelf-life of a carbonated liquid inexpensive, less difficult, and more accurate.
Throughout the description of this invention, reference is made to carbon dioxide dissolved in a liquid in a bottle. That the invention can be applied to other gases dissolved in liquids in other types of thin-walled containers will, however, be apparent to the reader.